WASHINGTON — The White House asserted Monday that it's highly likely that Syrian President Bashar Assad's regime, not the rebel opposition, was behind any chemical weapons use in Syria. Responding to weekend airstrikes in Syria, the White House also reiterated its view that Israel has the right to protect itself against weapons that could pose a threat to Israelis.

White House spokesman Jay Carney says there is certainly evidence that chemical weapons have been used in Syria. And on Sunday, a member of a U.N. panel investigating events in Syria said there were indications that rebel forces had used the nerve agent sarin.

But Carney questioned that claim.

"We are highly skeptical of suggestions that the opposition could have or did use chemical weapons," he said. "We find it highly likely that any chemical weapon use that has taken place in Syria was done by the Assad regime. And that remains our position."

Carney's comments came as Syria remained one of the most high-profile issues confronting the administration. Air strikes over the weekend on alleged Hezbollah-bound weapons in Syria and the status of chemical weapons use kept the country's civil war at the forefront. Lebanon's Hezbollah militia is an ally of Syria and foe of Israel.

The weekend airstrike on a military complex near the Syrian capital of Damascus killed at least 42 Syrian soldiers, a group of anti-regime activists said Monday, citing information from military hospitals.

The Israeli government has not formally confirmed that it carried out the air strikes Friday and Sunday, and Carney referred specific questions about the strikes to Israel.

"Israel certainly has the right to be concerned about the transfer of sophisticated weapons to Hezbollah," Carney said. "And that has been a concern of Israel's for a long time. The transfer of sophisticated weapons to terrorist organizations like Hezbollah is certainly a concern and a threat to Israel, and they have the right to act in their own sovereign interest on ... in response to those concerns."

Asked whether the U.S. had been forewarned about the strikes, Carney said: "We are in close coordination as a matter of course with the Israelis, and continue to be."

Carney says the U.S. is still looking for conclusive evidence about chemical weapons use in Syria. He said there is no timeline for the investigation.

Secretary of State John Kerry was leaving for Moscow on Monday to discuss the situation in Syria with Russian President Vladimir Putin.

"We have consistently, in our conversations with the Russians and others, pointed clearly to Assad's behavior as proof that further support for the regime is not in the interest of the Syrian people or in the interest of the countries that have in the past supported Assad," Carney said. "We have been clear in the past about our disappointment with Russia over their opposition to resolutions at the Security Council with regards to this matter. But this is an ongoing conversation."